1. Field of the Invention
This invention relates to a trigger device for a vehicle safety apparatus such as a vehicle air bag apparatus.
2. Description of the Prior Art
Japanese published examined patent application 59-8574 discloses an air bag trigger control apparatus in which the speed of the related vehicle is derived from a vehicle acceleration signal by an integrating process. In the apparatus of Japanese application 59-8574, when an integration value corresponding to the derived vehicle speed exceeds a given value, a related air bag is triggered. Generally, vehicle collisions are of various types, such as a head-on type, an oblique type, a pole-against type (a collision against a pole), and an offset type. During a collision of the vehicle, the acceleration of the vehicle varies in a manner which depends on the type of the collision. In the apparatus of Japanese application 59-8574, it is generally difficult to accurately and promptly detect vehicle collisions of some of the types.
Japanese published unexamined patent application 3-114944 discloses an air bag control apparatus in which a signal representing the acceleration of a related vehicle is processed to detect a collision of the vehicle. In the apparatus of Japanese application 3-114944, a quantity of a variation of the speed of the vehicle is calculated by integrating the vehicle acceleration signal, and a collision of the vehicle is detected on the basis of information representing the vehicle speed variation quantity and also information representing the difference between maximal and minimal values of the acceleration of the vehicle. The apparatus of Japanese application 3-114944 does not consider a differential of the vehicle acceleration signal in detecting a collision of the vehicle. Therefore, in the apparatus of Japanese application 3-114944, it is generally difficult to discriminate between a head-on collision and a rear-end collision. In addition, it is difficult to accurately and promptly detect vehicle collisions of some of the types.
U.S. Pat. No. 3,762,495 discloses a device for triggering a motor vehicle safety apparatus. When the related motor vehicle collides with another object, the device of U.S. Pat. No. 3,762,495 detects the impact between the motor vehicle and the other object and supplies a triggering signal to the safety apparatus in accordance with both the magnitude of deceleration resulting from the impact and the rate of the deceleration. The device of U.S. Pat. No. 3,762,495 does not integrate a vehicle acceleration signal for the detection of the collision between the motor vehicle and the other object. Accordingly, in the device of U.S. Pat. No. 3,762,495, it is generally difficult to accurately and promptly detect vehicle collisions of some of the types.
U.S. Pat. No. 4,994,972 discloses an apparatus for actuating a passenger restraint system in a passenger vehicle. In the apparatus of U.S. Pat. No. 4,994,972, a sensor senses vehicle deceleration and provides a deceleration signal having a value which varies in accordance therewith, and a plurality of crash evaluation circuits each respond to the deceleration signal for evaluating the deceleration signal in accordance with respectively different crash evaluation algorithms. Each evaluation circuit provides a vote signal when its evaluation of the deceleration signal indicates that the restraint system should be actuated. The vote signals are summed to provide a summation signal. The summation signal has a fractional value dependent upon the ratio of the number of vote signals to the total number of evaluation votes. The restraint system is actuated when the summation signal exceeds a threshold level. In the apparatus of U.S. Pat. No. 4,994,972, the value of an integral of the deceleration signal and the value of a differential of the deceleration signal are used for the generation of the vote signals. Specifically, the value of an integral of the deceleration signal is compared with a given value for the generation of the related vote signal while the value of a differential of the deceleration signal is compared with a given value for the generation of the related vote signal. The apparatus of U.S. Pat. No. 4,994,972 considers the value of a differential of the deceleration signal which occurs at the present moment, but does not consider the value of a differential of the deceleration signal which occurs before the present moment. Accordingly, in the apparatus of U.S. Pat. No. 4,994,972, it tends to be difficult to accurately and promptly detect vehicle collisions of some of the types.